diff --git a/list/list.js b/list/list.js
index b92c778..dc8d209 100644
--- a/list/list.js
+++ b/list/list.js
@@ -341,6 +341,7 @@ var eventsProtoSymbols = ("getOwnPropertySymbols" in Object) ?
 
 eventsProtoSymbols.forEach(function(sym) {
   Object.defineProperty(DefineList.prototype, sym, {
+  	configurable: true,
     enumerable:false,
     value: define.eventsProto[sym],
     writable: true